Ambient-Oriented Programming

User Tools

Site Tools

Trace:
at:tutorial:objects

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revisionPrevious revision
Next revision		Previous revision
Next revisionBoth sides next revision
at:tutorial:objects [2007/06/29 14:44] – jorgeat:tutorial:objects [2007/07/02 13:29] – jorge
Line 48: Line 48:
  
 Every object understands the message ''new'', which creates a clone (a shallow copy) of the receiver object and initializes the clone by invoking its ''init'' method with the arguments that were passed to new (''aX'' and ''aY'' in the example of the ''point'' object). Hence, the ''init'' method plays the role of “constructor” for AmbientTalk objects. AmbientTalk’s object instantiation protocol closely corresponds to class instantiation in class-based languages, except that the new object is a clone of an existing object, rather than an empty object allocated from a class. Every object understands the message ''new'', which creates a clone (a shallow copy) of the receiver object and initializes the clone by invoking its ''init'' method with the arguments that were passed to new (''aX'' and ''aY'' in the example of the ''point'' object). Hence, the ''init'' method plays the role of “constructor” for AmbientTalk objects. AmbientTalk’s object instantiation protocol closely corresponds to class instantiation in class-based languages, except that the new object is a clone of an existing object, rather than an empty object allocated from a class.
 +
 +AmbientTalk also provides a ''clone'' language contsruct which only creates a clone of the receiver object without calling the ''init'' method (as a matter of fact the ''new'' message desribed above does nothing more but invoking this construct and the ''init'' method subsequently).
 +
 +<code>
 +> def clonedPoint := clone: point
 +</code>
  
 ===== Delegation and cloning ===== ===== Delegation and cloning =====
-AmbientTalk features object inheritance or delegation. By means of delegation, an object can reuse and extend the defintion of another establishing a parent-child relationship. We identify two kinds of delegation relationships: **IS-A** and **SHARE-A**. These relationships define two different semantics for clonning child objects. Whereas clonning a **IS-A** child also clones its parent, **SHARE-A** child shares the parent of the cloned object.+AmbientTalk features object inheritance or delegation. By means of delegation, an object can reuse and extend the defintion of another establishing a parent-child relationship. We identify two kinds of delegation relationships: **IS-A** and **SHARE-A**. These relationships define two different semantics for clonning child objects. Whereas clonning a **IS-A** child also clones its parent, **SHARE-A** child shares the parent of the cloned object (see the figure below). 
 + 
 + 
 +{{:at:tutorial:isaversussharea.png|:at:tutorial:isaversussharea.png}} 
  
 The following code shows how to extend objects with a **IS-A** relationship. It uses the ''extend: with:'' language construct. The following code shows how to extend objects with a **IS-A** relationship. It uses the ''extend: with:'' language construct.
Line 90: Line 100:
 </code> </code>
  
-===== First-class Delegation =====+===== First-class delegation ===== 
 +AmbientTalk provides an explicit delegation operator ''^''. The code below illustrates the use of this operator in the implementation of the ''init'' method of the ''point3D'' object.
  
 +<code>
 +> def point3D := extend: point with: {
 +    def z := 0;
 +    def init(aX, aY, aZ) {
 +      super^init(aX, aY);
 +      z := aZ;
 +    };
 +  }
 +</code>
 +
 +A message sent to an object using this symbol (e.g. to the parent object in the example above) will first look for the method that matches the selector indicated in the message in this object (and its parents) and then execute the method body in the lexical scope of the message sender.
  
 ===== Encapsulation ===== ===== Encapsulation =====
-In AmbientTalk, all fields and methods are "public" via selection. Still, a field or method can be made "private" by means of lexical scoping. The following code shows the definition of an object inside the definition of a function. As such, the fields and methods of this object cannot be accessed directly from outside the funuction.+In AmbientTalk, all fields and methods are "public" via selection. Still, a field or method can be made "private" by means of lexical scoping. The following code shows the definition of an object inside the definition of a function. The fields and methods of this object cannot be accessed directly from outside the funuction.
  
 <code> <code>
Line 104: Line 126:
 </code> </code>
  
-This instruction fails:+Due to the encapsulation of this object the following instruction fails:
  
 <code> <code>
Line 111: Line 133:
   <object:5068254>   <object:5068254>
 </code> </code>
- 
- 
at/tutorial/objects.txt · Last modified: 2013/05/17 20:23 by tvcutsem